Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Thousands	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Common Stock in Treasury [Member]	Total
Beginning Balance at Dec. 31, 2011	$ 380	$ 317,329	$ 329,981	$ (6,104)	$ (103,476)	$ 538,110
Net income	0	0	41,442	0	0	41,442
Cash dividends	0	0	(19,966)	0	0	(19,966)
Purchase of treasury shares	0	0	0	0	(15,490)	(15,490)
Net issuance of shares for acquisition	13	25,811	0	0	0	25,824
Net issuance of shares to employee benefit plans and other stock plans, including tax benefit	0	(764)	(196)	0	1,785	825
Stock-based compensation	0	3,558	0	0	0	3,558
Other comprehensive (loss) income	0	0	0	2,358	0	2,358
Ending Balance at Sep. 30, 2012	393	345,934	351,261	(3,746)	(117,181)	576,661
Beginning Balance at Dec. 31, 2012	393	346,692	357,558	(5,880)	(116,490)	582,273
Net income	0	0	43,822	0	0	43,822
Cash dividends	0	0	(24,334)	0	0	(24,334)
Purchase of treasury shares	0	0	0	0	(12,459)	(12,459)
Net issuance of shares for acquisition	104	225,447	0	0	(5,779)	219,772
Net issuance of shares to employee benefit plans and other stock plans, including tax benefit	0	(2,469)	0	0	2,623	154
Stock-based compensation	0	3,571	0	0	0	3,571
Other comprehensive (loss) income	0	0	0	(17,240)	0	(17,240)
Ending Balance at Sep. 30, 2013	$ 497	$ 573,241	$ 377,046	$ (23,120)	$ (132,105)	$ 795,559